Incentive concealed by conductor? Rachmaninoff's backing! (6)
I believe the answer is:
carrot
'incentive' is the definition.
(as in a carrot and stick)
'concealed by conductor? rachmaninoff's backing' is the wordplay.
'concealed' indicates a hidden word.
'backing' says the letters should be written backwards.
'torrac' is hidden within 'by conductor rachmaninoffs'.
'torrac' backwards is 'CARROT'.
(Other definitions for carrot that I've seen before include "Pointed vegetable" , "One prov. used to encourage" , "Red vegetable used as inducement" , "Orange vegetable" , "Obstacle in race" .)